This application is the national phase of international application PCT/GB98/01712 filed Jun. 12, 1998 which designated the U.S.
This invention relates to a method for preparing exfoliated vermiculite particles for the manufacture of a finished product.
It is known to manufacture composite board products from exfoliated vermiculite particles. It is also known from WO 96/13468 to impregnate vermiculite with an impregnating composition comprising inter alia an isocyanate thermosetting resin, or to treat vermiculite particles with a dry powder novolac thermosetting resin.
There is a requirement that these products be highly water resistant.
According to a first aspect of the invention there is provided a method of manufacturing a finished product from exfoliated vermiculite particles which method includes the steps of:
(a) impregnating the exfoliated vermiculite particles with an impregnating composition comprising;
(i) a mineral oil; and
(ii) a liquid thermosetting resin and, if necessary, a catalyst therefor;
in the form of a dispersion of the liquid resin in the mineral oil; and
(b) compressing the exfoliated vermiculite particles with heating to allow the mineral oil to infuse the exfoliated vermiculite particles and to polymerise the thermosetting resin to form the finished product.
The method of the invention preferably includes a further step, step (c):
(c) before step (a) or preferably before step (b) applying to the exfoliated vermiculite particles a thermosetting resin in finely divided dry powder form and, if necessary, a catalyst therefor, so that the thermosetting resin in finely divided dry powder form adheres to the surfaces of the exfoliated vermiculite particles.
It is to be noted that the impregnating composition does not contain a solvent, which gives the method certain advantages, including the fact that there is no need to remove a solvent before step (b) can be carried out.
The thermosetting resin used in step (a) must be a liquid thermosetting resin so that it can infuse the exfoliated vermiculite particles and so that a dispersion of the resin in the mineral oil is formed.
The thermosetting resin used in step (a) is preferably an isocyanate thermosetting resin or a precursor thereof, more preferably a resin derived from diphenylmethane-4,4xe2x80x2-diisocyanate (MDI).
The thermosetting resin in finely divided dry powder form used in step (c) is preferably a novolac resin, based upon phenol and formaldehyde.
The liquid thermosetting resin used in step (a) is preferably used in an amount of from 1% to 20% inclusive by mass of the mass of the dry exfoliated vermiculite particles, preferably from 2% to 10% inclusive by mass of the mass of the dry exfoliated vermiculite particles.
The mineral oil is preferably used in an amount of from 5% to 30% inclusive by mass of the mass of the dry exfoliated vermiculite particles, more preferably in an amount of from 10% to 20% by mass of the mass of the dry exfoliated vermiculite particles.
The thermosetting resin in finely divided dry powder form used in step (c) may be used in an amount of from 0% to 20% inclusive by mass of the mass of the dry exfoliated vermiculite particles, preferably in an amount of from 3% to 10% inclusive by mass of the mass of the dry exfoliated vermiculite particles.
In step (a) the exfoliated vermiculite particles may be impregnated with the impregnating composition in any suitable manner, for example by spraying or coating the impregnating composition onto the exfoliated vermiculite particles, or by mixing the impregnating composition with the exfoliated vermiculite particles in conventional mixing equipment.
In step (b), the impregnated exfoliated vermiculite particles may be compressed and heated in a suitable press or mould at temperatures between 120xc2x0 C. and 250xc2x0 C. inclusive preferably up to 220xc2x0 C. and pressures of from 2 to 70 kg/cm2 inclusive preferably from 10 to 60 kg/cm2 inclusive for a time from 5 seconds to 20 seconds inclusive per mm of thickness, to allow the mineral oil to infuse the exfoliated vermiculite particles and to polymerise the thermosetting resin or resins present.
There may be added to the exfoliated vermiculite particles, an amount of organic or morganic fibres, preferably ceramic glass or carbon fibres, or synthetic, e.g polypropylene, polyethylene, acrylonitrile, or polyester fibres, or natural fibres, e.g sisal, kenaf, hemp, or flax fibres to provide improved internal bonding, and, where necessary, improved screw holding capability. The amount of fibres so added may be up to 7.5% by mass of the mass of exfoliated vermiculite particles.
According to a second aspect of the invention there is provided a method of preparing exfoliated vermiculite particles for the manufacture of a finished product, which method includes the step of:
(a) impregnating the exfoliated vermiculite particles with an impregnating composition comprising:
(i) a mineral oil; and
(ii) a liquid thermosetting resin and, if necessary, a catalyst therefor;
in the form of a dispersion of the liquid resin in the mineral oil.
The method may include a further step, step (c), before or after step (a):
(b) before or after step (a) applying to exfoliated vermiculite particles a thermosetting resin in finely divided dry power form and, if necessary, a catalyst therefor so that the thermosetting resin in finely divided dry powder form adheres to the surfaces of the exfoliated vermiculite particles.